1. Field of the Invention
This invention relates to film takeup spools for cameras.
2. Description of the Prior Art
In order to provide for quick loading of photographic film in the camera there has been provided a takeup spool which automatically grasps the film at a film leader thereof. In an example of a conventional takeup spool use is made of frictional means such as rubber pads. Because such a device is very susceptible to the influence of ambient temperature and humidity so that quick loading of the film can sometimes fail, there is thus lacking sufficient reliability.
In another example of a conventional spool the frictional rubber pads are replaced by pawls on the outer periphery of the sleeve hub of the spool. This automatic film takeup spool is, however, complicated in structure, unstable in its diameter of convolution of the film because of the positioning of a space for the pawls outside the sleeve hub, and apt to scratch the film surface as the film is being wound. With such situations in consideration, therefore, an attempt has been made to put the pawls inside the sleeve hub, for example, as shown in FIG. 1. This spool structure takes the form of an inner sleeve 2 having a great number of yieldable pawls 2a with their teeth 2b at the bottom ends thereof. These teeth 2b extend through respective square openings 1a of the sleeve hub 1 and project radially outwardly thereof into the perforations of the film when the film is engaged. After the film is wound up for some length, the tension of the film pushes the teeth 2b inwardly. Such a device, however, has disadvantages in that a sufficient grasping force is not always exerted on those of the teeth 2b which penetrate the perforations of film when the winding of the film starts, and that even after the film is wound to a certain diameter, those teeth 2b engaging the perforations of the film remain projected outwardly. Therefore, the wound film is caused to swell in diameter at this point, and the film will be damaged. Thus, the above-mentioned drawbacks are not all eliminated. In particular, the longer the length of projection of the tooth 2b as measured from the sleeve hub 1 is for the purpose of improving the quick engagement with the perforations of the film, the more this tendency is intensified. Though this tendency can be diminished by reducing the length of projection of the teeth 2b, an alternate problem arises in that there is a strong probability that the once established engagement of the teeth 2b with the perforations of film will be broken whereby a quick loading of the film can no longer be achieved.